JP3228743B2 - High corrosion resistance α-sialon sintered body and method for producing the same - Google Patents

Abstract

A highly corrosion-resistant alpha -sialon sinter comprising substantially an alpha -sialon composition represented by Mx(Si, Al)12(O, N)16 (wherein M represents at least one alpha -sialon-soluble element selected from the group consisting of Yb, Er and Dy; and 0 < x </= 0.8) and Sc2O3, which is insoluble in the alpha -sialon composition, in an amount of 0.01 to 15 wt.% based on the sinter, said sinter containing a Sc2O3-SiO2 composite (with a molar ratio of Sc2O3 to SiO2 of 1/0.1 to 1/50) as a grain boundary phase. The sinter has such a high corrosion resistance as to withstand the use in an environment where not only mechanical characteristics such as strength and toughness but also corrosion resistances such as oxidation resistance and chemical resistance are required.

Description

Description: TECHNICAL FIELD The present invention relates to a highly corrosion resistant α-sialonic conjugate having high corrosion resistance and a method for producing the same.

BACKGROUND ART Silicon nitride, which is a promising ceramic as a high-temperature structural material, is difficult to sinter. Conventionally, a sintered body is manufactured using an oxide such as Y ₂ O ₃ or Al ₂ O ₃ as a sintering aid. That is common. By using these sintering aids, densification by normal-pressure sintering is achieved, and application to complicated-shaped parts is possible. Well, the inventors of the present invention relate to an α-sialon sintered body, and disclosed in Japanese Patent Application Laid-Open Nos. 60-260471, 60-260472 and 61-91065, a mechanical sintering method using a normal pressure sintering method. It discloses that a sintered body having excellent mechanical properties can be obtained.

However, such a silicon nitride-based sintered body usually has
Oxide-based auxiliaries are contained in a total amount of about 10% by weight, and often remain as grain boundary phases in the sintered body. In the α-sialon sintered body, a similar phenomenon that a part of the solid solution element remains at the grain boundary is considered. The presence of the grain boundary phase in the sintered body is one of the causes of the decrease in high-temperature strength and corrosion resistance when using silicon nitride ceramics as a high-temperature member. Research on the crystallization of the interphase has been actively conducted.

For example, W. Braue et al., Proc. Of International Sym
posium on Ceramics Components for Engine, 1986
In FRG, 503 pp to 510 Section, have reported an improvement in high temperature strength due to _{Y 2 O 3, Al 2 O} 3 grain boundary crystallization of silicon nitride to sintering aid.

α-SiAlON has Al at the Si position in the α-Si ₃ N ₄ crystal structure.
However, at the same time as the substitution of O at the N position,
It is a substance having a structure in which metal elements such as Li, Mg, and Y penetrate and form a solid solution, and have a feature of being stable at high temperatures. The metal element which penetrates and forms a solid solution is usually added in the form of an oxide, but a part of the oxide does not form a solid solution but remains as a grain boundary phase. The starting material, silicon nitride, contains several percent of SiO ₂ as an impurity due to surface oxidation or the like. Such SiO ₂ reacts with Y ₂ O _3, which is a solid solution element of α-sialon, and the like. It is often known that these grains remain as grain boundary phases, and the presence of these grain boundary phases is a factor that causes a decrease in high-temperature characteristics and a decrease in corrosion resistance.

To date, there has been no study for improving the properties such as reduction of the amount of the grain boundary phase or crystallization treatment.However, as a result of the inventors' earnest studies, crystallization treatment and the like have led to improvement of the high-temperature strength properties. Is effective, but when oxidized at a temperature of 1200 ° C. or more for a long period of time, foaming occurs and cracks are generated on the surface.

The present invention solves the problems as described above, not only mechanical properties such as strength and toughness, but also high corrosion resistance that can withstand use in an environment where corrosion resistance such as oxidation resistance and chemical resistance is required. An object of the present invention is to provide an α-sialon sintered body and a method for producing the same.

The present inventors have conducted intensive studies in order to solve the above-mentioned problems, and as a result, this time, Sc ₂ O _{3 which} cannot be dissolved in α-sialon
And an α-sialon composition composed of silicon nitride, aluminum nitride, and an oxide of a metal element M (where M represents Yb, Er or Dy), molded, and then heated to 1600 ° C. in a non-oxidizing atmosphere. The sintered body obtained by sintering at a temperature within the range of 2000 ° C., and the sintered body obtained by further heat-treating the sintered body as required, are excellent not only in mechanical properties but also in corrosion resistance. I found that.

DISCLOSURE OF THE INVENTION The present invention has a composition formula: Mx (Si, Al) ₁₂ (O, N) ₁₆ , wherein M is at least one kind of α-sialon solid solution element selected from the group consisting of Yb, Er and Dy. And 0 <x
≦ 0.8, and 0.01 to 15% by weight, based on the weight of the sintered body, of Sc ₂ O ₃ which is insoluble in the α-sialon composition. And containing, as a grain boundary phase, a Sc ₂ O ₃ —SiO ₂ composite in a molar ratio of Sc ₂ O ₃ to SiO ₂ in the range of 1: 0.1 to 1:50. -To provide a sialonoid conjugate.

As used herein, the term “α-sialon composition” includes not only an α-sialon crystal phase single phase but also an α-sialon crystal phase and a β-silicon nitride crystal phase composite structure. These crystalline phases or composite structures may be those formed by sintering the raw material mixture,
Alternatively, the crystal phase or the composite composition may be already formed at the stage of the raw material mixture before sintering.

By the way, in silicon nitride and aluminum nitride raw materials,
Usually, it contains oxygen as an unavoidable anionic impurity. The β-silicon nitride crystal phase described in this specification is intentionally made of Al ₂ O ₃ or SiO _{2 for the} purpose of producing β-SIALON.
Excluding the case where is added, a crystal phase in which such unavoidable anionic impurities are dissolved is also included.

Α constituting a part of the α-sialon crystal of the present invention
The sialon composition is represented by the composition formula Mx (Si, Al) ₁₂ (O, N) ₁₆ ;

In the formula, M is a metal element that penetrates and forms a solid solution in α-sialon, and an element selected from the group consisting of Yb, Er, and Dy is used in the present invention. Among these solid solution elements, Yb is particularly preferable in the present invention. These metal elements dissolved in α-Si ₃ N _4, α- sialon together with stabilizing and reacts with Sc ₂ O ₃ is immiscible components described below, the containing Sc ₂ O ₃ Two phases are formed. Here, the term "second phase" is used to generically refer to phases other than the sialon composition of the sialon-based sintered body of the present invention.

Further, the value of x in the above formula indicates the solid solution amount of the metal element M, and 0 <x ≦ 0.8, preferably 0.1 ≦ x ≦
It is a number in the range of 0.5, more preferably 0.1 ≦ x ≦ 0.4. The value of x can be one factor that determines the composition range of the crystal phase in the α-sialon composition, and when the value of x is within the range of 0 <x ≦ 0.3, The α-sialon composition represented by the composition formula has a composite structure of an α-sialon crystal phase and a β-silicon nitride crystal phase, and when the value of x is in the range of 0.3 ≦ x ≦ 0.8, The α-sialon composition becomes a single phase of the α-sialon crystal phase. That is, the stable region of α-sialon is in the range of 0.3 <x ≦ 0.8, and x = 0.3 is α-sialon.
This corresponds to the lower limit of solid solution of sialon, and in the region of x <0.3, a mixture of stabilized α-sialon (x = 0.3) crystal phase and β-silicon nitride crystal phase is obtained.

This time, in the present invention, the above-mentioned α-sialon composition is treated with a specific amount of Sc which cannot be dissolved in the α-sialon composition.
It was found that when sintered together with ₂ O ₃ , the corrosion resistance of the obtained sintered body was significantly improved. The content of Sc ₂ O ₃ constituting the sintered body of the present invention together with the α-sialon composition is 0.01 to 15% by weight, preferably 0.01 to 10% by weight, more preferably 0.05 to 10% by weight based on the weight of the sintered body. -5% by weight. If the content of Sc ₂ O ₃ is less than 0.01% by weight, the effect of the addition of Sc ₂ O ₃ is weak, and if it exceeds 15% by weight, the hot strength decreases and the oxidation resistance becomes poor.

is one nitride compounds silicon raw material for producing α- sialon composition is usually a SiO ₂ containing about several% as unavoidable impurities by surface oxidation or the like, the SiO ₂ is typically
Yb ₂ O ₃ , Er ₂ O _{3 as} sources of solid solution elements of α-sialon
And / or reacts with Dy ₂ O ₃ and remains in the grain boundary phase.

On the other hand, according to the present invention, the α-sialon composition has
- When sintering with the addition of Sc ₂ O ₃ which can not be dissolved in sialon composition, Sc ₂ O ₃ plays a role of a sintering aid, suitable for promoting the densification of the sintered body obtained In addition to contributing, some of the added Sc ₂ O ₃ is the SiO ₂ remaining in the grain boundary phase.
Reacts to form a Sc ₂ O ₃ —SiO ₂ composite in the grain boundary phase.
The high corrosion resistance of the sintered body of the present invention is such Sc ₂ O
It is thought to be caused by the formation of the grain boundary phase structure composed of the _3- SiO ₂ composite.

From the phase equilibrium diagram of the Sc ₂ O ₃ -SiO ₂ system, the liquid phase formation temperature is a high melting point of 1660 ° C or higher, but such a method is necessary to improve not only the corrosion resistance of the sintered body obtained but also the high temperature characteristics. It is necessary to form a high melting point grain boundary phase.

Sc ₂ O ₃ pairs of Sc ₂ O ₃ -SiO ₂ complex to form a grain boundary phase
The ratio of SiO ₂ is generally at a molar ratio of 1: 0.1 to 1: may be in the range of 50. When the molar ratio is less than 1: 0.1, the hot strength of the obtained sintered body is small, and when it exceeds 1:50, Sc ₂ O ₃
The effect of the addition becomes weak, and the densification of the sintered body becomes insufficient. Accordance connexion, Sc ₂ O ₃ pairs SiO ₂ molar ratio of 1: 0.2 to 1: 50, especially 1:
Preferably it is in the range of 0.4 to 1:40. The amounts of Sc ₂ O ₃ and SiO _{2 in} the grain boundary phase can be determined by an analytical electron microscope. The Sc ₂ O ₃ to SiO ₂ molar ratio of the Sc ₂ O ₃ —SiO ₂ composite in the grain boundary phase can be adjusted by, for example, adjusting the amount of Sc ₂ O ₃ added or the oxygen in the silicon nitride raw material. This can be done by controlling the amount.

The α-sialon sintered body provided by the present invention is:
For example, it can be manufactured as follows.

First, silicon nitride predetermined ratio to produce the indicated is α- sialon composition by the composition formula, aluminum nitride, and _{Yb 2 O 3, Er 2 O} 3 and at least one oxide selected from Dy ₂ O _3, In addition, a predetermined amount of Sc ₂ O ₃ which does not form a solid solution with the α-sialon composition is mixed. Where Yb ₂ O ₃ , Er ₂ O ₃ , Dy ₂ O ₃
And as the Sc ₂ O _3, it is also possible to use precursor compounds which may vary in these oxides the firing conditions. Mixing ball mill, may be carried out using a vibration mill or the like, it is preferable to carried out in this case in an organic solvent to prevent oxidation of the raw material powder, also, Al ₂ O ₃ from crushing balls or the like
In order to avoid contamination, it is desirable to use a ball, container or resin container made of α-sialon. The resulting mixture is granulated and dried using a spray drier or the like to obtain a raw material for molding.

As a molding method, for example, mold molding, isostatic press molding, injection molding and the like can be used. Since the obtained molded body usually contains an organic component such as a binder, it is subjected to a degreasing treatment before sintering. Next, the molded body is heated at 1600 ° C. in a non-oxidizing atmosphere.
Sintering is performed at a temperature in the range of 20002000 ° C., and the sintering temperature is preferably in the range of 1600 ° C. to 1800 ° C.,
The sintering time is usually 30 minutes to 10 hours. For sintering, a sufficiently dense sintered body can be obtained by normal pressure sintering, but HIP, gas pressure sintering, or hot pressing may be used as necessary.

The α-sialon-based sintered body of the present invention thus obtained has extremely excellent corrosion resistance such as oxidation resistance and chemical resistance. The sintered body of the present invention achieves this high corrosion resistance when Yb, Er and / or Dy is used as a metal element which penetrates and forms a solid solution in α-sialon. This means that, for example, when an oxidation test is performed, the sintered body of the present invention forms a dense and smooth oxide film on the surface after the oxidation test, and together with the effect of the addition of Sc ₂ O ₃ , has an excellent corrosion resistance. However, a sintered body formed by using a solid solution element other than the above generally causes phenomena such as foaming on the sample surface, resulting in poor corrosion resistance.

The α-sialon sintered body of the present invention is excellent in mechanical properties, for example, bending strength, toughness and the like, and has a bending strength exceeding 1200 MPa (JIS R1601, three-point bending). Not only chemical stability such as corrosion resistance,
One of the features of the α-sialon sintered body of the present invention is that it has excellent mechanical properties.

Further, according to the sintered body of the present invention, it has been clarified that the α-sialon content in the sintered body changes depending on the amount of Sc ₂ O ₃ added. For example, when the added amount of Sc ₂ O ₃ increases, the amount of the α-sialon crystal phase decreases. This is because the added Sc ₂ O ₃ is a solid solution component of α-sialon, Yb ₂ O ₃ , Er ₂ O
₃ or Dy ₂ O _3, which is considered to form a composite.This is due to the amount of α- in the sintered body depending on the amount of Sc ₂ O ₃ added.
This indicates that the amount of the sialon crystal phase can be controlled, whereby the characteristics of the sintered body can be controlled.

α-sialon is α corresponding to the solid solution amount x of the metal element M.
- ratio of sialon crystal phase and β- silicon nitride crystal phase changes, hardness accordingly, toughness, the mechanical properties such as strength changes, also be cowpea the addition of Sc ₂ O ₃ Similar Control becomes possible. The α-sialon composition is characterized by being particularly excellent in mechanical properties such as strength and toughness in a low solid solution region of X ≦ 0.3, but those having this composition region are generally difficult to sinter. However, in the sintered body of the present invention, Sc ₂ O ₃ functions as a sintering aid in the sintering process, so that sinterability is improved even in this composition region, high temperature characteristics, excellent corrosion resistance and There is an advantage that an α-sialon sintered body having excellent mechanical properties can be easily obtained.

EXAMPLES Next, the present invention will be described more specifically with reference to Example 1.

Example 1 Silicon nitride (average particle size: 1 μm, cation impurity content: 0.2% or less, oxygen content: 0.8%), aluminum nitride (average particle size: 1 μm, cation impurity content: 0.2% or less,
Oxygen content: 1.0%), Yb ₂ O ₃ , Er ₂ O ₃ , Dy ₂ O ₃ (average particle size: 1.2 μm, purity: 99.9%), Sc ₂ O ₃ (average particle size:
1.0 μm, purity: 99.9%) were blended at a composition ratio shown in Table 1 below and kneaded. Kneading is resinous pot and α
-Performed in a ball mill using sialon balls for 30 hours in ethanol. After drying the obtained mixture, the mixture was molded by a cold isostatic press at a pressure of 1.5 t / cm ² , and the obtained molded body was fired at 1700 ° C. for 5 hours in a nitrogen atmosphere to obtain a sintered body. The obtained sintered body was 3 × 4 by surface grinding.
A test piece of × 40 mm was manufactured, and a test for evaluating oxidation characteristics was performed. Oxidation test was carried out at 1400 ° C in air for 100 hours.
Evaluation was made on the basis of the oxidation weight increase value and appearance after the test.

Analysis of Sc, Si, etc. in the grain boundary phase was performed using an analytical electron microscope.

The results are shown in Table 1. No. 1 to No. 7 are products of the present invention, and No. 8 to No. 10 are comparative examples.

From the results in Table 1, the oxidation weight gain of the α-sialon based sintered body of the present invention is excellent at 1.0 mg / cm ² or less,
It can be seen that the sample after the oxidation test was also covered with a smooth oxide film without foaming or the like. On the other hand, in the case of using Y as a solid solution element or in the comparative example in which Sc ₂ O ₃ was excessively added, the oxidation increase value was large.

Example 2 Silicon nitride (average particle size: 0.8 μm, cation impurity content: 0.2% or less, oxygen content: 1.2%), aluminum nitride (average particle size: 1.0 μm, cation impurity content: 0.2% or less) , Oxygen content: 1.0%), Yb ₂ O ₃ , Er ₂ O ₃ , Dy ₂ O ₃ (average particle size: 1.2 μm, purity: 99.9%), Sc ₂ O ₃ (average particle size: 1.0 μm) , Purity: 99.9%) were mixed at the same composition ratio as in Example 1 and kneaded.

The kneading was carried out by using a resin pot and α-sialon balls in a vibration mill for 20 hours in ethanol. The mixture is dried using a spray drier and then molded with a cold isostatic press at a pressure of 1.5 t / cm ² , and the obtained molded body is placed in a nitrogen atmosphere at 1750 ° C. under a pressure of 9.8 kgf / cm ² for 3 hours. It was heated and sintered.

A 3 × 4 × 40 mm test piece was prepared from the obtained sintered body,
Evaluation of bending strength (normal temperature and 1250 ° C) and an oxidation test were performed.

The bending test was performed by three-point bending with a span of 30 mm, and the oxidation test was performed under the same conditions as in Example 1. Table 2 shows the results. From the results in Table 2, it can be seen that the α-sialon sintered body of the present invention has a small decrease in strength during hot and has excellent high-temperature characteristics. On the other hand, as shown in the comparative examples, those using Y as a solid solution element have a large oxidation weight increase, and when Sc ₂ O ₃ is excessively added, the strength is significantly reduced during hot working.

INDUSTRIAL APPLICABILITY As described above, the α-sialon sintered body of the present invention has excellent corrosion resistance, high temperature properties, mechanical strength, and the like. For example, valve parts, engine members, machine tool parts ,
Useful in cutting tools and the like.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-56-129667 (JP, A) JP-B-63-37075 (JP, B1) (58) Fields investigated (Int. Cl. ⁷ , DB name) C04B 35/599

Claims (6)

(57) [Claims] 1. A composition formula: Mx (Si, Al) ₁₂ (O, N) ₁₆ , wherein M is at least one selected from the group consisting of Yb, Er and Dy.
Species of α-sialon solid solution element, and 0 <x ≦ 0.
8, and 0.01 to 15% by weight, based on the weight of the sintered body, of Sc ₂ O ₃ which cannot be dissolved in the α-sialon composition. And, as a grain boundary phase, a high corrosion resistance α- characterized by containing a Sc ₂ O ₃ -SiO ₂ composite in a molar ratio of Sc ₂ O ₃ to SiO ₂ of 1: 0.1 to 1:50. Sialonic conjugate. 2. The sintered body according to claim 1, wherein the solid solution element M is Yb. 3. The sintered body according to claim 1, wherein the value of x is within a range of 0.1 ≦ x ≦ 0.4. 4. The sintered body according to claim 1, wherein Sc ₂ O ₃ is contained within a range of 0.05 to 5.0% by weight based on the weight of the sintered body. 5. The sintered body according to claim 1, wherein the molar ratio of Sc ₂ O ₃ to SiO ₂ in the Sc ₂ O ₃ —SiO ₂ composite is in the range of 1: 0.4 to 1:40. 6. A predetermined proportion of silicon nitride, aluminum nitride, and Yb ₂ O ₃ , Er ₂ O ₃ and Dy ₂ O ₃ which form an α-sialon composition represented by the composition formula according to claim 1. At least one oxide selected from the group consisting of: and a mixture comprising 0.01 to 15% by weight of Sc ₂ O ₃ based on the weight of the sintered body,
The method for producing an α-sialonic conjugate according to claim 1, wherein the sintering is performed at a temperature in the range of 1600 ° C to 2000 ° C in a non-oxidizing atmosphere.